Most telephone sets equipped with microphones and speakers for use in a hands-free mode, such as a speaker phone, have preset factory settings for defining an operating range of a microphone (“MIC”). An engineering design team tries to anticipate all types of user conditions when establishing factory presets. Thus, the presets are a compromise of settings to allow the phones to work adequately under most conditions.
Factors that affect the detection of a signal at the receive end, such as signal to noise ratio (SNR), background noise (BGN) and echo, vary depending on the operating range of the microphone with respect to a user. To save processor overhead, several preset levels are fixed in engineering design, with levels of factors such as SNR, BGN and echo predetermined for varying conditions, ranging from a close range setting to a far range setting. For example, in a close range setting, a user is assumed to be near a microphone and background noise level is set as “low.” In contrast, in a far range setting, a user is assumed to be far from a microphone and a background noise level is set as “high.”
Adjustments among the several preset levels ranging from close to far range typically occur automatically and out of the user's control. Accordingly, the actual performance may be less than optimal. For example, if a processor selects a close range setting, sensitivity of the pickup is defined in the preset as “low” and a user must be close to the microphone for reasonable sound levels at the receiving end. Such an automatic setting may limit the usefulness for large group participation. On the other hand if the sensitivity is defined as “high,” the microphone may pick up environmental noise, such as a radio or TV in the background, which will be difficult to filter out without compromising the transmitted signal.
In a conventional system, a user may alter the final transmission gain stage by adjusting the transmission (speaker) volume control. However, the user cannot set a sensitivity and selectivity of the receive (MIC) circuit.
Thus, what is desired is a system for allowing a user to have some degree of control over the operating range for the MIC by setting the sensitivity and selectivity of the MIC circuit and thus control the ambience which will be perceived by the listener at the other end of the call.